Thanks for a swift reply!
I still have to wait for my posts to be approved, and in the meantime I managed it. I've attached how I did it for some critiquing if anyone feels like it. It works, but it may not be best practice. I'm going to look into the method you described, however.
As for E-stops, the machine is fitted with them! This is purely for the speed signal, feeding into a driver card that is only enabled/disabled via the machine. The PLC is essentially a pretty but overpriced potentiometer. The business gets what the business wants though...
Thanks again.
When MB15 (my hmi stop button) is pressed, and the speed is anything but 0, the stop cycle latches on with MB20.
Once latched, a 1 second timer is started, and it checks whether we need to increment or decrement to reach zero, and starts the next process. If at zero, it removes the stop latch at MB20
If decrement is required, after the 1 second timer is up, we decrement the speed setting by 1, and reset the 1 second timer. But because the stop cycle is latched, after another second we decrement again. When 0 is reached as above, we reset the stop cycle. Rinse repeat for Increment.